Soap-thickened grease modified with glycerine ester of a low molecular weight carboxylic acid



United States Patent SOAP-THICKENED GREASE MODIFIED WITH GLYCERINE ESTER OF A LOW MOLECULAR ,WEIGHT CARBOXYLIC ACID No Drawing. Application February 27, 1953 Serial No. 339,460

8 Claims. (Cl. 252-405) The present invention relates to improved lubricating greases. More particularly, the invention deals with lllbl'lcating greases having high dropping points and high structural stability when subjected to high rates of shear, such as encountered in certain large roller bearings. In its broadest aspect, the invention pertains to greases of this type thickened with a soap-type grease thickener and mixed with a small proportion of an ester of glycerine, which contains at least two moles of a low molecular weight carboxylic acid per mole of glycerine.

Heretofore greases having desirable high temperature properties, such as dropping points above 500 F. and high stability to mechanical working have been prepared by using the alkali or alkaline earth metal soaps and salts of combinations of high and low molecular weight carboxylic acids. An outstanding example are the greases obtained by subjecting rapeseed oil to alkali fusion in a lubricating oil vehicle at temperatures of about 450- 500 F. Thickeners for similar greases combining high mechanical stability with high dropping points may be made by alkali fusion of other glycerides or neutralization or saponification of various materials containing high and low molecular weight carboxylic acids.

Greases of this type require relatively large amounts of soap thickener to alford the desired high dropping points. The finished grease usually hardens excessively under high ratesof shear such as encountered in certain large roller bearings and in certain homogenizing equipment, such as the Manton-Gaulin homogenizer. As the thickeners are diluted with lubricating oil, i.e. as the soap concentration of the grease decreases, the dropping point is lowered and semi-fluid products of poor structuralstability result. Simple-soap type greases behave in a generally analogous manner.

It has now been found that greases combining high dropping points and desirable structure with excellent stability to mechanical working, particularly at high rates of shear may be obtained by adding to the grease a small proportion of a dior tri-e ster of glycerine with a low molecular Weight aliphatic monocarboxylic acid having about 1-5 carbon atoms, such as formic, acetic, propionic, butyric, valeric, furoic, acrylic acids, etc. Triacetin, i.e. glycerine tn'acetate is the preferred glycerine ester although glycerine diacetate and other similar glycerine esters may be used.

" The amount of glycerine ester added to the grease, in

ICE.

ferred to add the glycerine ester prior or during the cooking or fusion stage of the grease, appreciable improvements may be obtained even if the glycerine ester is added to the cold grease after completion of this cooling process but prior to grease homogenization or working at high rates of shear.

In either case, it has been found that the glycerine ester acts to increase the original hardness of the grease somewhat. However, it also substantially reduces the hardening elfect of mechanical working particularly under high rates of shear. Neither glycerine alone nor metal salts of low molecular weight aliphatic acids have similar effects on grease exposed to high rates of shear, the former normally acting as a softening agent and the latter tending to increase the hardening tendency of the grease when added to high molecular weight fatty acid soaps.

The present invention 'may be applied to soap-thickened greases of all types containing metal soaps of high molecular weight fatty acids having 10-30 carbon atoms per molecule, such as stearicacid, oleic acid, behenic acids, hydrogenated fish oil acids, etc., as well as soap-salt complexes of similar soaps with metal salts of low molecular weight aliphatic acids, such as formic, acetic, propionic and acrylic acids, etc. While greases prepared by alkali fusion of rapeseed oil in lubricating oil at temperatures up to about 500 F. are preferred, other complex soapthickened greases, such as those obtained by alkali fusion of other fats and oils of animal or vegetable origin including castor oil, cottonseed oil, sperm oil, etc., at temperatures as high as 580 F. may be used.

Metal bases suitable for the formation of the greases of the invention include the hydroxides of alkali and alkaline earth metals, such as lithium, sodium, potassium, calcium and barium. However, alkali metal bases, particularly sodium hydroxide, are preferred.

Regarding lubricating oil bases suitable for the greases of this invention, all types of mineral lubricating oils as well as synthetic oils, including di-esters, complex esters, formals, hydrocarbon polymers and other materials having lubricating oil characteristics may be used. Thickener concentrations may vary between about 5 and 40 wt. pere cent of the finished grease. It is, however, one ofthe advantages of the present invention that greases of highly desirable dropping points and structural characteristics may be obtained on the basis of substantially reduced thickener concentrations. Thus, highly useful greases containing as little as 5-25 wt. percent of'soap may take the place of greases containing as much as 20-40 wt. percent of soap.

Greases in accordance with the invention maybe prepared by intimately mixing about 0.1-2 wt. percent of a preformed dior tri-ester of glycerine with a low molecaccordance with the invention, need not substantially exceed' 3. wt. percent of the total charging formulation of the grease or about 5 wt. percent of the grease thickener. 'Less than 0.1 moleof the glycerine ester per mole of high molecular weight fatty acidin the grease is normally suflicient for the purposes of the invention. An eflfective working range is about 0.1-2 wt. percent of glycerine ester and preferably about 0.5-1.5 wt. percent, particularly in the case of triacetin, based on total grease formulation.

a The glycerineester should be added to the grease prior to final homogenization of the latter. While it is preular weight aliphatic acid into a soap-thickened grease of the type specified at substantially atmospheric temperatures. For this purpose the grease and ester may be mixed in a conventional grease kettle, followed by more intimate mixing in a mill or homogenizer.

However, the preferred method of the invention involves incorporation of the glycerine ester into the grease prior to the completion ofthe compounding stage, For this purpose, the preformed glycerine ester may be added to the original charging stock of the grease prior to cooking or at any stage of the cooking process including the cooling stage. -When preparing greases by alkali fusion of rapeseed oil in accordance with the preferred embodiment of the invention, a suitable mixture of rapeseed oil, lubricating oil, sodium hydroxide and preformed glycerine ester may be heated to about 280-320 F. while stirring, the alkali normally being used in the form of an aqueous solution of about 30-50% concentration. When dehydration is complete,j more lubricating oilImay be added and heating is continued to about'460--500 F.

EXAMPLE I Charging formulation: Wt. percent Rapeseed oil 18.00 Petroleum sodium sulfonate 0.80 NaOH (as 40% solution) 3.97 Triacetin 1.00

Blend of naphthenic type mineral oil distillates, having a viscosity of 50 S.S.U. at

210 F. 74.72 Phenyl alpha-naphthylamine 1.01 Di-salicyl aldehyde propylene diamine 0.50

Preparation All the rapeseed oil, sulfonate, triacetin, NaOH (as 40% aqueous solution) and about /3 of the mineral oil were charged to a gas fired kettle and heated to 300 F. while mixing thoroughly. At this stage some more of the mineral oil (13.8%) was added and the heating and mixing was continued to amaximum temperature of 470 F. At about 380 F. a secondary reaction took place in which some moisture was liberated and the number of small bubbles formed indicated that some light gas, probably hydrogen, was also liberated. The rest of the mineral oil was added at 470 F. to 460 F. while the inhibitors were added after cooling down to 260 F. The mixing was continued while cooling to 185 F. at which temperature the grease was packaged.

EXAMPLE II Another grease was prepared containing no triacetin but otherwise the same ingredients and amount of ingredients as shown in Example I, except also that 75.72% of the mineral oil was employed as compared with 74.72% in Example I. The grease in this case was heated to a maximum temperature of 500 F. as is customary when preparing this type of grease from rapeseed oil.

Samples of greases preparedin Examples 1 and II were exposed to very high rates of shear by passing them 5 times through a Gaulin homogenizer at 5,000 p.s.i.g. By such treatment rapeseed oil greases of the type here involved are usually hardened to their ultimate hardness or lowest worked penetration values. A comparison of these two greases is shown below:

It is apparent from the above comparison that the grease of the invention (Example I) in addition to its higher dropping point is much less detrimentally affected by high mechanical stresses than a similar grease made without the addition of triacetin.

EXAMPLE III A grease was prepared by cooking 22.0% rapeseed oil with 4.8% NaOH in the presence of 1.0% petroleum sodium sulfonate and naphthenic lubricating oil of the type used in Examplesl and No triacetin was used, The

final grease contained 24.1% soap and had a worked penetration of 226 mm./ 10 and a dropping point of 464 F. On homogenizing this grease, 5 passes at 5,000 p.s.i.g., the grease was hardened to a worked penetration of 169 mm./l0.

To this grease was added /2% triacetin at room temperature, prior to homogenization. After homogenizing the mixture, 5 passes at 5,000 p.s.i.g., the grease had a worked penetration of 148 mm./l0. This shows that triacetin also is a useful hardening and thickening agent for grease manufacture even without cooking it in the presence of soap.

When, instead of /z% of triacetin, 1% of glycerine was added to this grease in the same manner, the worked penetration, after homogenization 5 passes at 5,000 p.s.i.g., rose from 169 to 211 indicating the softening or plasticizing effect of glycerine as such, as distinguished from the hardening eifect of triacetin.

The invention is not limited to the specific figures of the foregoing examples. The relative proportions of the grease constituents may be varied within the limits indicated above to obtain greases of different consistency and varying characteristics.

What is claimed is:

1. The method of preparing lubricating greases which comprises subjecting in a major proportion of a mineral lubricating oil a saponifiable material selected from the group consisting of fats and fatty oils of animal and vegetable origin to alkali fusion at a temperature of about 450 to 580 F. in grease making proportions in the presence of about 0.1 to 2.0 wt. percent of a compound selected from the group consisting of diand triesters of glycerine with low molecular weight aliphatic monocarboxylic acids having from about 1 to 5 carbon atoms per molecule, cooling and intimately mixing the product.

2. The method of claim 1 in which said material is rapeseed oil.

7 3. The method of claim 2 in which said compound is triacetin.

4. The method of preparing lubricating greases which comprises subjecting in a major proportion of a mineral lubricating oil a saponifiable material selected from the group consisting of fats and fatty oils of animal and vegetable origin to alkali fusion at a temperature of about 450 to 580 F. in grease making proportions, cooling the product, and adding to the cooled product about 0.1 to 2.0 wt. percent of a compound selected from the group consisting of diand tri-esters of glycerine with low molecular weight aliphatic monocarboxylic acids having 1-5 carbon atoms per molecule.

5. The method of claim 4 in which said material is rapeseed oil and said compound is triacetin.

6. The grease produced by the method of claim 5.

7. The method of preparing an improved lubricating grease which comprises thickening a lubricating oil to a grease consistency by dispersing therein a grease thickener selected from the group consisting of (1) a metal soap selected from the group consisting of alkali metal and alkaline earth metal soaps of C to C fatty acids, and (2) the alkali fusion reaction product of an alkali and a saponifiable material selected from. the group consisting of fats and fatty oils of animal and vegetable origin heated to a temperature in the range of 450 to 580 F., and adding 0.1 to 2.0 weight percent of a compound selected from the group consisting of diand tri-esters of glycerine with an aliphatic carboxylic acid having from 1 to about 5 carbon atoms per molecule.

8. An improved lubricating grease composition comprising lubricating oil thickened to a grease consistency with a thickener selected from the group consisting of (1) a metal soap selected from the group consisting of alkali metal and alkaline earth metal soaps of C to C fatty acids, and (2) the alkali fusion reaction product of an alkali and a saponifiable material selected from the group consisting of fats and fatty oils of animal and vegetable origin heated to a temperature in the range of 450 to 580 F., and about 0.1 to 2.0 weight percent of a compound selected from the group consisting of diand tri-esters of glycerine with an aliphatic carboxylic acid having from 1 to about 5 carbon atoms per molecule.

References Cited in the file of this patent UNITED STATES PATENTS 6 Wiezevich et a1 Apr. 30, 1940 Schott et al. July 4, 1950 Carmichael et a1 Aug. 14, 1951 Morway et a1 Aug. 28, 1951 Armstrong Mar. 15, 1955 Morway et a1 Aug. 14, 1956 OTHER REFERENCES Organic Chem, by Paul Karrer, 3rd English ed. 1947,

Wiezevich et a1. Feb. s, 1938 pub. by Elsenier Pub. Co. Inc., N. Y., page 183. 

1. THE METHOD OF PREPARING LUBRICATING GREASES WHICH COMPRISES SUBJECTING IN A MAJOR PROPORTION OF A MINERAL LUBRICATING OIL A SAPONIFIABLE MATERIAL SELECTED FROM THE GROUP CONSISTING OF FATS AND FATTY OILS OF ANIMAL AND VEGETABLE ORIGIN TO ALKALI FUSION AT A TEMPERATURE OF ABOUT 450* TO 580* F. IN GREASE MAKING PROPORTIONS IN THE PRESENCE OF ABOUT 0.1 TO 2.0 WT. PERCENT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF DI- AND TRIESTERS OF GLYCERINE WITH LOW MOLECULAR WEIGHT ALIPHATIC MONOCARBOXYLIC HAVING FROM ABOUT 1 TO 5 CARBON ATOMS PER MOLECULE, COOLING AND INTIMATELY MIXING THE PRODUCT. 